As known, many private telecommunications systems are currently available which are generally referred to as Professional Mobile Radio (PMR) systems, i.e. mobile radio systems for professional users, such as police corps, building staff, rescue services, etc.
Current PMR systems typically comprise one or more repeaters (base stations) and a plurality of mobile devices, also referred to as mobile terminals, which can communicate with one another and with the base stations within the VHF (Very High Frequency) or UHF (Ultra High Frequency) bands.
As far as performance is concerned, the PMR systems currently in use allow their users, equipped with respective mobile devices, to communicate with one another even when they are many kilometers apart, i.e. they allow to obtain wide coverage areas.
Communication takes place when the mobile devices gain access to a radio channel shared by the mobile devices themselves. For security reasons, this access is granted to enabled mobile devices only, so that closed groups of users of corresponding PMR systems are formed; the management of said groups, i.e. the administration of user permissions, may also take place dynamically.
Unlike cellular networks, wherein communications are of the point-to-point type, i.e. the data is sent by a first mobile device and received by a second mobile device only, in PMR systems communications are generally of the point-multipoint type, i.e. the data is sent by a first mobile device and received by all other mobile devices belonging to the same group. Moreover, communications are typically of the “push to talk, release to listen” (PTT) type, i.e. a mobile device gains access to the radio channel when the user presses a push-button available on the mobile device itself.
Within the frame of the above-mentioned PMR systems, communications among different mobile devices occur in compliance with communication standards such as, for example, the Terrestrial Trunked Radio (TETRA) standard, the Project 25 standard and the MPT1327 standard (first generation trunked radio standard).
The TETRA standard requires a network infrastructure, also known as Switching and Management Infrastructure (SwMI), comprising a network of base stations (BS) and configured for arbitrating the communications among the various mobile devices by allocating corresponding radio resources.
According to the TETRA standard, different radio interface types, i.e. different communication modes (protocols), may be used, among which: a direct mode (Direct Mode Operation, DMO), wherein mobile devices establish communications directly between each other; an infrastructural or trunked mode (Trunked Mode Operation, TMO), wherein mobile devices communicate exclusively through the network infrastructure SwMI; a repeater mode, wherein a mobile device acts as a repeater of signals emitted by mobile devices operating in DMO mode, thus widening the network coverage; and a gateway mode (Gateway Mode Operation, GMO), wherein a mobile device acts as an intermediary between a group of mobile devices operating in DMO mode and a group of mobile devices operating in TMO mode. There are also TETRA radio interfaces optimized for voice and data traffic (voice plus data, V+D) and for data packet traffic (packet data optimized, PDO); in particular, in the case of a mobile device implementing a V+D radio interface, the mobile device will operate in “trunking” mode, i.e. it will use and release the radio channel in a dynamical manner, thereby allowing the radio channel to be effectively shared by different user groups.
Thanks to the presence of a network infrastructure, PMR systems compliant with the TETRA standard typically offer the following services to their users: group voice calls in half-duplex and PTT mode, emergency calls, dynamic group management, hierarchical communication management by means of priority mechanisms, and digital data transmission, though at low bit rates. In particular, the TETRA standard allows compliant mobile devices to operate as cellular telephones, i.e. terminals connected to the Public Switched Telephone Network (PSTN) through the SwMI network infrastructure, as well as to make group calls through the election of a “dispatcher”, i.e. a mobile device adapted to distribute the signals emitted by the single mobile devices to other mobile devices belonging to the same group.
The Project 25 communication standard, commonly used in North America, is similar to the TETRA standard and comprises eight different communication interfaces. Mobile devices compliant with the Project 25 standard can communicate with traditional radio equipment in analog mode and with one another both digitally and analogically. In particular, communications among mobile devices take place by default through the mediation of a repeater, although the Project 25 standard also includes a mode called “talk around” according to which mobile devices can communicate directly without requiring the mediation of a network infrastructure.
Finally, the MPT1327 standard is a communication standard for industrial PMR systems. In addition to mobile devices, it also requires the presence of a system controller (trunking system controller) and a network infrastructure. In more detail, PMR systems compliant with the MPT 1327 standard comprise multiple radio channels, one of which is defined as a control channel (CC), whereas the remaining channels are defined as traffic channels (TC). Communications between mobile devices and network infrastructure take place over the control channel, while communications between mobile devices take place over traffic channels, thus allowing for both point-to-point calls and group calls.
The above-mentioned communication standards provide group communications over large geographical areas, but they offer no support for localizing the mobile devices, nor they allow for digital communications at high bit rates.
In order to overcome these drawbacks, and in particular to increase the speed of transmission of digital data, enhanced communication systems have been proposed which integrate mobile devices of the aforementioned type together with broadband devices, i.e. devices capable of providing digital communications at high bit rates, e.g. devices supporting the Wireless Local Area Network (WLAN) technologies.
So-called Mobile Ad-Hoc Networks (MANET) have also been developed, which are networks of mobile devices, commonly referred to as nodes, that implement a coordination algorithm in a distributed or centralized manner so as to carry out those functions traditionally performed by a network infrastructure, e.g. data routing. Said networks of mobile devices can also operate in the absence of any external infrastructure, but they provide no information to the users about the position of the other users, and therefore they do not provide mutual localization of the mobile devices, thus being unsuitable for professional use, which requires a prompt localization of users possibly in trouble.
On the other hand, mobile radio communication devices are known which comprise localization apparatuses such as, for example, the Global Positioning System (GPS) or simpler Radio Frequency Identifier (RFID) labels. Mobile radio communication devices are also known which are integrated into GSM (Global System for Mobile communications) systems, and which allow to estimate the position of a cellular telephone based on the identifier of the cell in which the cellular telephone is located.
For example, patent application U.S. Pat. No. 6,373,430 describes a portable GPS/radio unit communicating through a wireless network with at least one second unit which sends radio signals indicating its own position. The GPS/radio unit comprises a GPS receiver configured for receiving satellite signals from a plurality of satellites, a radio receiver configured for receiving radio signals sent by the second unit, a processor configured for calculating the position of the unit depending on the incoming satellite signals and for identifying the position of the second unit on the basis of the incoming radio signals, and a screen configured for showing the position of the second unit.
Similarly, patent application EP1162474 describes a portable apparatus comprising a GPS-type positioning device capable of communicating its own current position to another portable apparatus. The apparatus also comprises a device adapted to acquire a geographical map and a screen adapted to show the current position of another portable apparatus with reference to said geographical map.
Instead, patent application EP1576386 describes a cartographic localization device fitted with a screen, a keyboard, wireless communication means and GPS localization means. Known mobile devices, also including therefore the devices described in EP1576386, EP1162474 and U.S. Pat. No. 6,373,430, as well as the corresponding systems consisting of mobile devices and a network infrastructure, suffer from several drawbacks. In particular, in the case of mobile devices using the GPS system, localization is very accurate due to the utilization of GPS receivers, which however require adequate visibility of the sky vault in order to be able to receive and correlate the signals coming from the satellite constellation. Vice versa, in the case of low-cost mobile devices using RFID labels, localization is only possible over small areas, since RFID labels draw little power and the emitted signals cannot reach distances longer than a few meters. Finally, localization systems based on GSM networks are often affected by considerable inaccuracy, which makes them unsuitable for professional use; furthermore, they can only be implemented by telephone companies, since the mapping of the cells of a GSM network is not of public knowledge.
Also, the mobile devices known in the art can only determine their own and other mobile devices' geographical positions in the presence of a localization system, whether satellite or terrestrial type. For this reason, communication and localization systems comprising mobile devices like those described above are not generally suitable for use within closed spaces or where there is no network coverage. Moreover, the close dependence of the systems described above on the presence of network coverage makes them unsuitable for use in emergency situations, wherein no service provision uncertainty due to possible network coverage interruptions is admissible.
It is the object of the present invention to provide a mobile communication and localization device which at least partly overcomes the drawbacks of the prior art.
The present invention discloses a mobile communication and localization device as set out in claim 1.